We use cookies to give you the best experience possible. By continuing we’ll assume you’re on board with our cookie policy

See Pricing

What's Your Topic?

Hire a Professional Writer Now

The input space is limited by 250 symbols

What's Your Deadline?

Choose 3 Hours or More.
Back
2/4 steps

How Many Pages?

Back
3/4 steps

Sign Up and See Pricing

"You must agree to out terms of services and privacy policy"
Back
Get Offer

Synthesis of Benzocaine Essay

Hire a Professional Writer Now

The input space is limited by 250 symbols

Deadline:2 days left
"You must agree to out terms of services and privacy policy"
Write my paper

A. Introduction/Aims:

The aim of the current investigation is to investigate the acid-catalysed Fischer esterification mechanism underlying the synthesis of the anaesthetic benzocaine using p-aminobenzoic acid and ethanol in excess. The resulting synthesised compound was subject to IR and melting point analyses in order to determine the identity and indeed the purity of the obtained sample.

Don't use plagiarized sources. Get Your Custom Essay on
Synthesis of Benzocaine
Just from $13,9/Page
Get custom paper

Benzocaine exhibits two main components common to the anaesthetic family: (1) an aromatic system usually having directly attached an ester and (2) a one to four unit hydrocarbon chain.

The ester group is essential in body detoxification of this substance due to enzymatic cleavage of the ester linkage. Other anaesthetics may also contain a tertiary amine functional group which translates into the compound being soluble in the body.

B. Stoichiometric Equations:

C. Reactant table:

Reactant/product

M.W. (g mol-1)

Quantities used/obtained

Moles used/obtained

Mole ratio theoretical/actual

4-aminobenzoic acid

137.14

5.00 g

0.036

1/1, limiting

Ethanol

46.07

65 mL = 51.42 g

1.12

1/31.1, in excess

Sulfuric acid

98.08

5 mL = 9.15 g

0.093

Benzocaine

165.19

4.05 g

0.025

0.025/0.036 = 0.69

The limiting reagent of this reaction is p-aminobenzoic acid.

Thus the theoretical yield of benzocaine is expected to be 0.036 mols as a 1:1 ratio exists between and 4-aminobenzoic acid and benzocaine.

% yield = =

= 69 % (2 S.F.)

D. Procedure:

No changes were made to the procedure given in CHEM3061 Laboratory Manual, p. 1-1 to 1-2.

E. Results:

Addition of concentrated sulfuric acid to the p-aminobenzoic acid, ethanol mix generated a white solid precipitate to form.

Addition of 10% sodium carbonate solution to the refluxed solution above caused effervescing to occur.

The product appeared to be a white crystalline solid, tabular, semi-transparent with moderate reflectivity, ~5mm in width.

Weight of product = 4.05 g % yield = 69 %

Melting point range = 88 – 89 �C Literature melting point = 89 �C

F. IR analysis:

Frequency (cm-1)

Strength

Assignment

Comment

1633, 1593, 1574

Medium

C=C-C aromatic ring stretch –

This is an approximation for the unique aromatic ring bonding.

2984, 2957, 2899

Weak

Aromatic C-H stretching

Diagnostic region confirming aromaticity.

770, 669, 639

Medium to strong

C-H out of plane bending on an aromatic ring

Multiple band structures; less energy required for C-H bending than for the its stretching counterpart and thus comes at a lower frequency.

1123, 1108, 1078, 1024

Medium to strong

C-H in plane bending vibrations of aromatic compounds

845

Strong

1,4 di-substituted (para) phenyl

Single, strong band between 860 – 800 cm-1 provides evidence to support a para substituted phenyl.

3420

Medium

NH2 antisymmetric stretch

The asymmetric stretch is slightly higher in frequency than its symmetric counterpart as it requires more energy. Broad peaks due to H-bonding.

3339

Medium

NH2 symmetric stretch

3221

Medium

A smaller absorption near 3200 cm-1 is considered to be the result of interaction between an overtone of the 1600 cm-1 band with the symmetric N-H stretching band.

1272

Strong

Aromatic primary amine CN stretch

Strong absorption due to large dipole moment between C and N.

1679

Strong

Ester C=O stretch

Frequency observed is lower than normal ester C=O due to direct conjugation of the aromatic ring with the carbonyl.

1170

Strong

C -O stretch

Polar bond – large dipole moment; strong absorption.

G. 1H NMR Analysis

Chemical shift (ppm)

Multiplicity

Integration

Assignment of signals and explanation

1.35 (E)

Triplet

3.4 (3H)

CH3

Influenced to some extent by the electron withdrawing COO group causing deshielding and thus the chemical shift to move downfield from its original at approximately 0.8 ppm; this is an inductive effect.

4.10 (D)

Singlet

2.0 (2H)

NH2

Single peak observed in characteristic chemical shift region.

4.31 (C)

Quartet

2.0 (2H)

CH2

Influenced greatly by the electron withdrawing COO group causing deshielding and the chemical shift to move downfield from its original at approximately 1.2 ppm; this is an inductive effect.

6.63 (B)

Doublet of doublets

1.7 (2H)

H (B)

Influenced by the electron donating group NH2 which causes shielding and the chemical sift to move upfield of its original at approximately 7.2 ppm; this is a mesomeric effect. This effect obviously contributes more heavily than magnetic anisotropy, which in this case would produce the opposite effect; negative shielding would result, moving the signal downfield.

7.85 (A)

Doublet of doublets

1.8 (2H)

H (A)

Influenced by the electron withdrawing COO group causing deshielding and the chemical shift to move downfield from its original at approximately 7.2 ppm; this is an inductive effect. Also magnetic anisotropy causes negative shielding again contributing to the downfield move in chemical shift.

7.26

Singlet

N/A

CHCl3 – residual protonated solvent

H. Discussion:

The reaction mechanism for the synthesis of benzocaine is divided into six key steps: (1) the protonation of the carbonyl by sulfuric acid to give a resonance stabilised intermediate; NH2 is also protonated (2) nucleophillic attack of the alcohol at the carbonyl carbon (3) loss of oxonium leaving group (4) proton transfer leading to a tetrahedral carbonyl addition intermediate (5) further proton transfer leading to a new oxonium ion and its subsequent loss giving (6) the acidified product, water and regeneration of the acid catalyst; finally the product is neutralised with sodium carbonate.

An acceptable yield of 69% of benzocaine was achieved in the present experiment; product may have been lost through (1) the reversible nature of each step in the reaction, although this was minimised by employing Le Chatelier’s principle (using excess ethanol) and (2) during refluxing, a loss of solvent would lead to a significant decrease in yield.

The identity of the synthesised compound was confirmed through IR and melting point analyses to be that of benzocaine. In particular, the obtained IR spectrum iterated the presence of structures such as a 1,4 di-substituted aromatic ring, primary aromatic amine, and an ester functional group directly attached to the aromatic ring as a result of lower frequency of the carbonyl than expected due to conjugation from the aromatic ring. Furthermore, the melting point range achieved (88-89�C) concurred well with the literature value of 89�C, confirming the purity of the obtained sample.

Cite this Synthesis of Benzocaine Essay

Synthesis of Benzocaine Essay. (2017, Jul 22). Retrieved from https://graduateway.com/synthesis-of-benzocaine-227/

Show less
  • Use multiple resourses when assembling your essay
  • Get help form professional writers when not sure you can do it yourself
  • Use Plagiarism Checker to double check your essay
  • Do not copy and paste free to download essays
Get plagiarism free essay

Search for essay samples now

Haven't found the Essay You Want?

Get my paper now

For Only $13.90/page